Oxygen or oxygen-containing gas is injected into pig iron production units, in which carbon carriers are used to reduce iron-oxide-containing material to pig iron, in order to produce reducing gas and to provide heat required for the ongoing chemical and physical conversions by means of exothermic oxidation processes. For easier legibility, the terms “oxygen” and “oxygen-containing gas” are used as synonyms in the text which follows. Those parts of the devices for injecting oxygen which adjoin the reaction chamber of the pig iron production unit are exposed to high temperatures, and this makes it necessary to cool these parts intensively. In order to achieve particularly good heat dissipation during cooling, the nozzles for injecting oxygen are produced from copper or a copper alloy.
The problem which arises during operation of the pig iron production unit is that media are sucked up from the reaction chamber into the jet of oxygen at the high velocities at which oxygen is blown in, i.e. between 70 and 330 m/s. By way of example, these media are hot gases, particles of solid matter or particles of liquid matter such as molten iron or molten slag. The effect of the suction is that these media flow back counter to the flowing-out direction of the oxygen as far as the outlet edge of the oxygen channel of the nozzle. It has been shown that this results in hot gases and particles of solid matter and liquid matter being sucked into the oxygen channel, which leads to deposits in the oxygen channel and to thermal-abrasive wear of the nozzle. Hot gases which enter the oxygen channel lead to the build-up of resistance to the direction of oxygen flow, to heating of the oxygen, and therefore to thermal loading of the nozzle and thermally induced wear.
The advantage of using copper or a copper alloy as the nozzle material is that it can be effectively cooled owing to its thermal conductivity, but this also has the disadvantage that it can provide little resistance to thermal-abrasive wear owing to its strength. The wear has a negative effect in many ways. Firstly, it is necessary to exchange worn nozzles for maintenance, which means operational stoppages and therefore a drop in production. In addition, the reaction behavior in the pig iron production unit changes since the jet of oxygen penetrates to different extents into the reaction chamber given different shapes of the outlet edge; it becomes more difficult to plan production over a relatively long period of time due to fluctuations in the reducing time which are associated with wear of the outlet edge. In addition, the wear bears a considerable safety risk, since the nozzle is cooled with water. If the wear produces a leak in the cooling water channel, water may enter the reaction chamber and cause explosions.